It is desirable form metal replacement gate p-channel metal oxide semiconductor (PMOS) transistors to have gates with work functions greater than 4.85 electron-volts (eV) and more particularly work functions of approximately 5.10 eV. Oxygen atoms from the gate dielectric layers, especially those containing hafnium, diffuse into the metal gates, disadvantageously resulting in reduced work functions of the gates and higher threshold voltages of the PMOS transistors. Dielectric barrier layers which are thick enough to significantly reduce oxygen diffusion undesirably cause reduced gate dielectric capacitances and higher threshold voltages.